Heart transplantation is a therapeutic option in the management of end stage heart failure. Two methods of surgical transplantation are typically done; orthotopic or heterotopic. In the orthotopic technique, the donor heart is attached to a partial remnant of the recipient's native right and left atria, essentially replacing the recipient heart chambers. In the heterotopic technique, the donor heart is implanted along side and is attached to the recipient heart such that it augments the recipient's cardiac output. FIG. 1a shows what the completed surgical heterotopic transplant looks like, and FIG. 1b illustrates the orthotopic surgery.
Known problems with heterotopic transplant include the progressive deterioration observed in the recipient left ventricular function and reduced exercise capacity due to the competitive contraction of the two hearts; with the donor left ventricle generating a much higher afterload for the failing recipient left ventricle.
Additionally (in both described transplant techniques), the donor heart is denervated, therefore its resting rate (typically near 90 bpm) exceeds that of the recipient sinus rate. Further, the donor heart rate response to exercise is attenuated, if present at all. Finally, the recipient atrium often develops arrhythmias.
Similar problems may develop with xenotransplants, such as with the use of baboon hearts or genetically altered porcine hearts transplanted into humans.
Because of these and other potential problems, an implantable electrical stimulus generator could be useful if designed to meet the needs of this situation.
A modified pacemaker that can pace at multiple sites and preferably also sense at multiple sites can be used to alleviate the problems described in transplantation described above.
Cardiac electrical stimulation has a long history with implantable cardiac stimulators going back perhaps 40 years. Only recently however have the implanted devices found use for multiple lead configurations. Examples include patents assigned to ELA Medical (Limousin et al.) U.S. Pat. No. 5,514,161 and 5,584,867, for example, and there are also patents directed to defibrillators, see for example U.S. Pat. No. 5,282,837 issued to Adams et al. which show leads in the coronary sinus that may be useful in left atrial or left ventricular stimulation.
A typical pacemaker system which could form the basis for most of the requirements for multisite pacing is described in U.S. Pat. No. 5,549,654 issued to Powell, although many other suitable pacing or pacing and/defibrillation implantable device pulse generator (IPG) platforms may be used. A number of designs for Cardiac Assistance devices may also be used. Such devices are described in, for example U.S. Pat. No. 4,411,268 to Cox, and are used in stimulating muscle tissue which has been (or will be) surgically wrapped around the heart while also providing the possibility of direct cardiac pacing. It is also known for example, that optimizing the timing of ventricular pulses, in relation to paced or serial atrial events can assist in Hypertropic Obstructive Cardiomyopathy (HOCM) Therapy. This is demonstrated in the pending PCT patent publication No. WO96/25977, published in August 1996, for example. Also, as described in the Limousin and Limousin et al. patents cited above, bi-atrial pacing can be advantageous.
It is currently recognized in theory that differing pathways for depolarization waves can greatly affect cardiac performance (see Fritz Prinzen, Ph.D. et al. American Heart Journal, 1995:130:1045-1053, for example). Accordingly, there is a need to develop a multisite capable fully configurable pacemaker and/or pacemaker/defibrillator. Of course, there have been numerous devices which have been taught or developed in response to this need, including those described in patents on devices to control ventricular activation sequence (Cohen, U.S. Pat. No. 5,267,289 and 5,174,536 and Goldreyer U.S. Pat. No. 4,365,639), devices for dealing with fibrillation and other arrhythmias (Combs U.S. Pat. No. 5,562,708; Hill U.S. Pat. No. 5,507,784 and 5,403,356; Zipes U.S. Pat. No. 5,366,486; Duffin U.S. Pat. No. 5,243,978; 5,209,229; Adams U.S. Pat. No. 5,158,079; Ideker U.S. Pat. No. 5,107,834; Tacker Jr U.S. Pat. No. 4,708,145 and 4,548,203; and Prystowsky U.S. Pat. No. 4,554,922), devices capable of sensing through multiple, sometimes switchable electrodes (King U.S. Pat. No. 4,630,611 and 4,754,753; Funke U.S. Pat. No. 3,937,226; and Rockland U.S. Pat. No. 4,088,140; Kahn U.S. Pat. No. 4,354,497;; Mower(in which multiple sense electrode sites assist in treating hemodynamic dysfunction) U.S. Pat. No. 4,928,688), devices for switching between stimulation electrodes generally, (for example, in upper airway muscle stimulation Kallok U.S. Pat. No. 5,281,219), in devices for switching between different out of the device sensors or electrodes (Schaldach U.S. Pat. No. 4,412,541); King U.S. Pat. No. 4,750,494; Peterson U.S. Pat. No. 5,447,519; and Yang U.S. Pat. No. 5,476,503), in a device for applying differing parts of a pulse segment to different parts of a defibrillation electrode (in Dahl U.S. Pat. No. 4,969,463), and in devices which use the same electrodes for demand pacing and antitachy breakup pulses (Kolenik U.S. Pat. No. 4,181,133). However none of the aforementioned devices can perform the function herein described and in various aspects they are lacking in the flexibility and ease of configuration or simplicity of circuitry as the device described herein.
Several doctors have attempted to solve these problems with conventional pacemakers. In AN EXAMPLE OF HOW TO PACE A PATIENT WITH A HEART TRANSPLANTATION, by Osterholzer et al., Journal of Heart Transplant 1988;7:23-5, the authors describe the use of a Pacesetter AFP/283, Pacesetter Systems Inc., pacemaker with a two lead system configured with a lead in the recipient atrium (orthotopic transplant) used to sense the native sinus rate and after the shortest programmable delay, pace the donor atrium, which was counted on to pace the donor ventricle. (An additional lead was implanted into a donor ventricle so that if "atrial fibrillation with slow ventricular response in the donor heart requires ventricular stimulation, a simple pulse generator exchange will solve the problem.")
Another study published by McClurken, et al., RECIPIENT-DONOR ATRIAL SYNCHRONIZATION BENEFITS ACUTE HEMODYNAMICS AFTER ORTHOTOPIC HEART TRANSPLANTATION in the Journal of Heart Lung Transplant, 1996; 15:368-70 also described the benefits of timing the donor atrium to follow the recipient sinus rate. The McCracken article limits it study to acute pacing benefits with temporary heart wires.
Kacet, et al., in their article BIPOLAR ATRIAL TRIGGERED PACING TO RESTORE NORMAL CHRONOTROPIC RESPONSIVE IN AN ORTHOTOPIC CARDIAC TRANSPLANT PATIENT, describe native sinus rhythm following set up for orthotopic transplants wherein a bipolar lead splitter is used to provide a way to bring one unipolar lead each to the native and donor atria, one to sense in the native atria and the other to pace in the donor heart. It cannot, of course sense in the donor atrium at all nor can it sense in the native atrium while the donor atrium is being paced. Kacet use this fact to enforce the employ of a long refractory period, which happens to miss some native atrial arrhythmia.
All the foregoing suggests the need for an advanced pacemaker designed to assist in maintaining hemodynamic and natural sinus rate pacing for transplant patients. It would be most beneficial if the pacemaker could be used in both ortho- and heterotopic transplants.
Further, since the advent of transplant monitoring by implantable devices as described for example in U.S. Pat. Nos. 5,402,794 issued to Wahlstrand, et al.,5,197,480(Gepphardt), 5,139,028(Steinhaus et al.),5,330,513(Nichols et al), 5,331,966(Bennett et al.), and 4,905,707(Davies and Lekholm), an additional benefit can be had from specifically designing a pacemaker for transplants. That is, by sending indications of the state of the transplanted heart, the usual monthly biopsies to determine the state of the transplant tissue can be avoided or ameileorated.
All of the references cited above are incorporated herein in their entireties by this reference so as to provide both background and disclosure for the invention described herein, said invention being described below with reference to the following Figures.